Methods of detachment of a layer from a wafer of material chosen from semiconductor materials is known, which includes:                creating a zone of weakness in the thickness of the wafer that defines the layer to be detached in the thickness of the wafer, and        subjecting the wafer to a treatment for effecting the detachment of the layer, at the level of the weakened zone.        
These methods permit thin layers to be obtained with a thickness on the order of a micron or less. The layer may be of a semiconductor material such as silicon. The SMART-CUT® method of S.O.I.TEC Silicon On Insulator Technologies S.A., is an example of this type of method making use of such steps. It is generally desired that the surface of the detached layers generally conform to strict surface state specifications. It is common to find specifications for surface roughness not to exceed 5 angstroms in rms (root mean square) value. Roughness measurements are generally performed using an atomic force microscope (AFM). With this type of apparatus, roughness is measured on surfaces scanned by the point of the AFM microscope, from 1×1 μm2 to 10×10 μm2, and more rarely, 50×50 μm2 or even 100×100 μm2.
It is also possible to measure surface roughness by other methods, such as by using a measurement of “haze”. This method has the advantage of permitting rapid characterization of the uniformity of roughness over the whole of a surface. The haze, measured in ppm, arises from a method using the optical reflectivity properties of the surface to be characterized, and corresponds to an optical “background noise” given off by the surface due to its micro-roughness.
It is also desirable that the roughness be as homogeneous as possible over the surface of the detached layer. Thus, similarly strict specifications may be associated with the remainder of the wafer after detachment (this remainder being termed the “negative”). It is possible to provide surface treatment steps after the detachment to attain these specifications.
These treatments may, for example, make use of polishing, sacrificial oxidation, and/or supplementary annealing steps.